The present invention relates generally to a speed or cruise control for a vehicle and more particularly to an adaptive or selftuning speed control which continuously tunes controller gain so as to optimize performance.
Speed control systems are well known today. Each such system maintains the vehicle at a substantially constant speed selected by the operator.
One significant objective in the design of a speed control system is acceptable performance over a wide range of vehicle lines and over a wide range of operating conditions (often referred to as "robustness"). In this context, performance is measured in terms of a speed tracking ability, throttle movement, steady state speed error, and frequency of recalibration.
In an attempt to achieve the foregoing objective, and to meet increasingly stringent performance requirements, speed control systems have become increasingly more complex through the years. The earliest systems simply held the throttle in a fixed position (J. T. Ball, "Approaches and Trends in Automatic Speed Controls," SAE Technical Paper #670195, 1967). In the late 1950's, speed control with feedback appeared These systems used proportional feedback of the speed error, and the controller gain typically provided full throttle in response to an error in the range of six to ten miles per hour (mph) (W. C. Follmer, "Electronic Speed Control," SAE Technical Paper #740022, 1974).
The next enhancement was proportional control with an integral preset. Then came proportional integral control systems, often referred to as P.I. systems (B. Chaudhare et al, "Speed Control Integrated into the Powertrain Computer," SAE Technical Paper #860480, 1986). The combination of proportional and integral feedback, with appropriate controller gains, substantially reduced speed droop when the system was initialized.
Further enhancements are described in U.S. Pat. Nos. 4,803,637; 4,870,583; and 4,893,243. In general, system performance is improved by switching controller gains to predetermined values in accordance with specific operating conditions.
With the recent availability of inexpensive microcontrollers, more sophisticated control strategies have been attempted These include proportional integral derivative, or P.I.D., control; optimal linear quadratic regulation (T. Tabe et al, "Vehicle Speed Control System Using Modern Control Theory," IEEE IECON '86 Proceedings, 1986); fuzzy logic control (M. Uriubara et al, "Development of Automotive Cruising Using Fuzzy Control System," Journal of SAE of Japan, Vol. 42, No. 2, 1989); and self-tuning control (T. Tsijii et al, "Application of Self-Tuning to Automotive Cruise Control," American Control Conference Proceeding, May, 1990).
The objective is, again, a robust, stable speed control system. The potential saving from a single generic system capable of providing acceptable performance across a wide range of vehicle lines and over a wide range of operating conditions is enormous.